Fluorescent four-ring symmetrical/unsymmetrical molecules containing alkyl chains of a varied number of –CH₂– groups with a bent-core have been synthesized to explore their liquid crystalline (LC) and photophysical properties. Some of these molecules depending upon their alkyl chain length were found to exhibit B1 and B7 liquid crystalline phases and are characterized by various analytical techniques such as FT-IR, ¹H NMR, mass, POM, DSC, single crystal XRD, etc. Crystal structure determination reveals the hydrogen bonded enol form of these molecules with non-planar bent-molecular geometry. Intramolecular hydrogen bonding was found to play an important role in the stabilization of these molecules and in the origin of their green photoluminescence (GPL). The photo-physical experimental results through various control experiments clearly demonstrate that the origin of the large Stokes shifted GPL of these molecules can be attributed to the excited state intramolecular proton transfer (ESIPT) process. The formation of various types of anionic species and their stability were explored through steady-state and time-resolved fluorescence measurements. These compounds are found to be good turn-on PL probes in the selective detection of zinc ions at the micromolar level. Upon binding of zinc ions with the bent-core molecule, the structural changes have been investigated through NMR spectroscopy.

中文翻译：

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具有ESIPT的四环弯曲核分子中的绿色光致发光的起源，通过开启发射选择性地检测锌离子及其液晶特性†

已经合成了包含具有弯曲核心的各种–CH _2-基团的烷基链的荧光四环对称/不对称分子，以探索其液晶（LC）和光物理性质。已发现其中一些分子取决于其烷基链长，表现出B1和B7液晶相，并通过各种分析技术进行了表征，例如FT-IR，¹ H NMR，质量，POM，DSC，单晶XRD等。晶体结构确定揭示了具有非平面弯曲分子几何形状的这些分子的氢键烯醇形式。发现分子内氢键在这些分子的稳定化及其绿色光致发光（GPL）的起源中起着重要作用。通过各种控制实验得到的光物理实验结果清楚地表明，这些分子的大斯托克斯位移GPL的起源可归因于激发态分子内质子转移（ESIPT）过程。通过稳态和时间分辨荧光测量，探索了各种类型的阴离子物质的形成及其稳定性。在微摩尔水平上选择性检测锌离子时，发现这些化合物是良好的开启PL探针。